Abstract This work presents a modeling and experimental analysis on the flame length of buoyant turbulent slot diffusion flame. An approximate predictive correlation of flame length is derived based on the governing equations. The role of initial momentum and buoyancy on flame length is quantitatively described by a modified Froude number Frm. The physical model indicates that the flame length of a turbulent slot flame is proportional to (Frm)1/3 and (Frm)0 respectively when the flame is buoyancy-dominated and momentum-dominated. The results, for the first time, give a physical verification on the previous scaling laws on buoyant turbulent slot flame in literature. Slot flame tests are conducted using two burners (for which the width W and length L are respectively 0.9 mm × 20.5 mm and 5.5 mm × 86 mm) and four kinds of high-purity hydrocarbon gas fuels (methane, acetylene, ethane and propane). Experimental data show that the radial temperature profiles of buoyant turbulent slot flames can be well described by a Gaussian function normalized by the temperature radius, which is independent of axial position and flame scale. Moreover, experimental data verify that the physical model applies for different fuel supply rates, types of fuels and flame scales. Additionally, the results indicate that the turbulent slot flame is buoyancy-dominated when Frm 107. Finally, it is indicated that the scale effect of turbulent slot flame is closely associated with the flame temperature under different flame scales.